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gh-159739: Bound encoding-name lookahead in surrogatepass #159785

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Merged
JelleZijlstra merged 1 commit into from
Oct 20, 2026
Merged

gh-159739: Bound encoding-name lookahead in surrogatepass #159785

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12 changes: 12 additions & 0 deletions Lib/test/test_codeccallbacks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -755,6 +755,18 @@ def test_badandgoodsurrogatepassexceptions(self):
(s[:1], 1 + n)
)

def test_surrogatepass_truncated_encoding_name(self):
handler = codecs.lookup_error('surrogatepass')
for width in (16, 32):
encoding = f'utf-{width}-'
data = (0xd800).to_bytes(width // 8, 'little')
for exc in (UnicodeEncodeError(encoding, '\ud800', 0, 1, 'test'),
UnicodeDecodeError(encoding, data, 0, len(data), 'test')):
with self.subTest(encoding=encoding, error=type(exc).__name__):
with self.assertRaises(type(exc)) as cm:
handler(exc)
self.assertIs(cm.exception, exc)

def test_badhandlerresults(self):
results = ( 42, "foo", (1,2,3), ("foo", 1, 3), ("foo", None), ("foo",), ("foo", 1, 3), ("foo", None), ("foo",) )
encs = ("ascii", "latin-1", "iso-8859-1", "iso-8859-15")
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.243aa8.rst
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@@ -0,0 +1,2 @@
Avoid reading past the end of an encoding name when the ``surrogatepass``
error handler receives a truncated UTF-16 or UTF-32 name.
6 changes: 4 additions & 2 deletions Python/codecs.c
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Expand Up @@ -1173,7 +1173,8 @@ get_standard_encoding_impl(const char *encoding, int *bytelength)
}
if (*encoding == '-' || *encoding == '_' )
encoding++;
if (Py_TOLOWER(encoding[1]) == 'e' && encoding[2] == '\0') {
if (encoding[0] != '\0' &&
Py_TOLOWER(encoding[1]) == 'e' && encoding[2] == '\0') {
if (Py_TOLOWER(encoding[0]) == 'b')
return ENC_UTF16BE;
if (Py_TOLOWER(encoding[0]) == 'l')
Expand All @@ -1192,7 +1193,8 @@ get_standard_encoding_impl(const char *encoding, int *bytelength)
}
if (*encoding == '-' || *encoding == '_' )
encoding++;
if (Py_TOLOWER(encoding[1]) == 'e' && encoding[2] == '\0') {
if (encoding[0] != '\0' &&
Py_TOLOWER(encoding[1]) == 'e' && encoding[2] == '\0') {
if (Py_TOLOWER(encoding[0]) == 'b')
return ENC_UTF32BE;
if (Py_TOLOWER(encoding[0]) == 'l')
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